This study mainly focuses on the diurnal and long-term variation characteristics of the calibration performance of the geostationary (GEO) meteorological satellite Fengyun-4A/ Advanced Geostationary Radiation Imager (FY-4A/AGRI) infrared (IR) channels from June 1, 2017 to December 31, 2020. An improved algorithm is developed in this research based on thein situobservations from ocean drifters, which can capture the diurnal variations of the calibration performance of FY-4A/AGRI IR channels. The results suggest that there are significant and nonnegligible diurnal variations of the uncertainties and biases for the brightness temperature (TB) observed by the FY-4A/AGRI, especially the IR channels at 3.71, 8.61, 10.83, and$12.07 \mu \text{m}$. Among them, the calibration performance from 16:00 to 18:00 UTC (around the time of local midnight at the subsatellite point of FY-4A) is worse at$3.71 \mu \text{m}$, while TB biases from 04:00 to 16:00 UTC are relatively large at$12.07 \mu \text{m}$. Moreover, after the operational calibration and update in June 2020, the long-term TB biases at channel 08 ($3.71 \mu \text{m}$) obviously decrease from about 5–2.5 K, and the TB biases at channel 14 ($13.54 \mu \text{m}$) increase from about 0.5–3 K, implying a possible positive or negative impact of the calibration update on the calibration performance of IR channels. Overall, this method based on thein situdrifter data can well monitor the on-orbit calibration performance of GEO satellite imaging sensor’s IR channels such as the FY-4A/AGRI, allowing an objective assessment on the effect of calibration update events.

Scalar multiplication is the most important and expensive operation in elliptic curve cryptosystems. In this study, the authors improve the efficiency of the elliptic net algorithm to compute scalar multiplication by using the equivalence of elliptic nets. The proposed method saves four multiplications by a constant in each iteration loop. Experimental results also indicate that the proposed algorithm will be more efficient than the previously known results on this line while it is still slower than the state‐of‐the‐art algorithm to compute scalar multiplication.

In this paper we propose a modified Elliptic Net algorithm to compute pairings. By reducing the number of the intermediate variables which should be updated in the iteration loop of the Elliptic Net algorithm, we speed up the computation of pairings. Experimental results show that the proposed method is more efficient than the original Elliptic Net algorithm on Barreto-Naehrig (BN) curves which are the best choice for implementing pairings at 128-bit security level.